Non-aqueous electrolyte for lithium-ion battery and lithium-ion battery

ABSTRACT

A non-aqueous electrolyte for a lithium-ion battery and a lithium-ion battery. The non-aqueous electrolyte comprises unsaturated phosphate compounds and unsaturated cyclic carboxylic acid anhydride compounds. The unsaturated phosphate compounds have the structure illustrated in structural formula 4; structural formula 4: R13, R11, and R12 are independently selected from hydrocarbon groups having 1-5 carbon atoms respectively, and at least one of R13, R11, and R12 is an unsaturated hydrocarbon group containing double bonds or triple bonds; the unsaturated cyclic carboxylic acid anhydride compounds have the structure illustrated in structural formula 5; structural formula 5: R14 is independently selected from vinylidene having 2-4 carbon atoms or fluoro-substituted vinylidene. By means of the synergistic effect of two compounds, the non-aqueous electrolyte has excellent high-temperature cycling performance and storage performance, and also has lower impedance and good low-temperature performance.

TECHNICAL FIELD

The present application relates to the field of lithium-ion batteryelectrolyte, and more particularly to a non-aqueous electrolyte forlithium-ion battery and a lithium-ion battery.

BACKGROUND OF THE INVENTION

Lithium-ion batteries have the characteristics of high specific energy,high specific power and long cycling life. They are presently mainlyused in the fields of 3C digital consumer electronics, new energy powervehicles, and energy storage. With the continuously increasedrequirements for the mileage of new energy vehicles and theminiaturization of digital consumer electronics products, high energydensity has become the main development trend of lithium-ion batteries.Increasing the operating voltage of lithium-ion batteries is aneffective way to increase the energy density of the batteries.

Increasing the operating voltage of a lithium-ion battery tends toresult in performance degradation. Because at high voltages, on the onehand, there is a certain instability in the crystal structure of thecathode of the battery, and structural collapse may occur in the processof charging and discharging, resulting in performance degradation; andon the other hand, at high voltages, the surface of the cathode is in ahighly oxidative state and has a high activity, such that it will easilycatalyze the oxidative decomposition of the electrolyte. Thedecomposition products of the electrolyte will easily deposit on thesurface of the cathode, blocking the deintercalation channels forlithium ions, thereby degrading battery performances.

The electrolyte is a key factor affecting the overall performances ofthe battery. In particular, the additives in the electrolyte areparticularly important for the performances of the battery. Therefore,in order to give full play to the performances of the power battery ofthe nickel-cobalt-manganese ternary material, the matching of theelectrolyte holds the key. The currently practical electrolytes forlithium-ion batteries are the non-aqueous electrolytes added with aconventional film-forming additive such as vinylene carbonate(abbreviated as VC) or fluoroethylene carbonate (abbreviated as FEC).The addition of VC and FEC ensures the excellent cycling performances ofthe batteries. However, VC has poor stability at high voltages, and FECtends to decompose and produce gas at high temperatures. Therefore,under high-voltage and high-temperature conditions, these additives aredifficult to meet the performance requirements of lithium-ion batteriescycling at high voltages and high temperatures.

Patent application No. 201410534841.0 discloses a triple bond-containingphosphate compound as a novel film-forming additive, which not onlyimproves the high-temperature cycling performance, but alsosignificantly improves the storage performance. However, researchers inthe art have found during researches that the triple bond-containingphosphate additive not only forms a film on the cathode, but also formsa film on anode. The film formation on the anode will significantlyincrease the impedance of the anode and significantly degrade thelow-temperature performance.

Cyclic unsaturated carboxylic anhydride compounds as a lithium batteryelectrolyte additive have also long been reported in some related papersand patents. Having similar functional characteristics to the triplebond-containing phosphates, the cyclic unsaturated carboxylic anhydridesalso significantly improve the high-temperature performance, but at thesame time, they will also increase the battery impedance, and degradethe low-temperature performance, restricting the application of thelithium-ion batteries with non-aqueous electrolyte under low temperatureconditions.

SUMMARY OF THE INVENTION

An object of the present application is to provide a non-aqueouselectrolyte for lithium-ion battery, as well as a lithium-ion batteryusing the non-aqueous electrolyte.

In order to achieve the above object, the present application adopts thefollowing technical solutions:

Technical Solution I:

In one aspect, the present application discloses a non-aqueouselectrolyte for lithium-ion battery, comprising an unsaturated phosphatecompound and a unsaturated cyclic carboxylic anhydride compound, theunsaturated phosphate compound having a structure represented byStructural Formula 4,

wherein R13, R11 and R12 are each independently selected from ahydrocarbon group having 1 to 5 carbon atoms, and at least one of R13,R11 and R12 is an unsaturated hydrocarbon group having a double bond ora triple bond; and

the unsaturated cyclic carboxylic anhydride compound having a structurerepresented by Structural Formula 5,

wherein R14 is selected from the group consisting of an alkenylene grouphaving 2 to 4 carbon atoms or an fluorinated alkenylene group having 2to 4 carbon atoms.

Generally, two kinds of additives with good high-temperatureperformance, high impedance and poor low-temperature performance, whenused in combination, can allow the battery to further obtain betterhigh-temperature performance, but the impedance will further increaseand the low-temperature performance will further deteriorate. However,researchers in the art have found during researches that when adding theabove-mentioned triple bond-containing phosphate compound and cyclicunsaturated carboxylic anhydride compound at the same time in anon-aqueous electrolyte for lithium-ion battery, in contrast to usingthe triple bond-containing phosphate compound alone, thehigh-temperature performance significantly improved, and unexpectedly,the interfacial impedance remarkably lowered, and the low-temperatureperformance remarkably improved.

The technical principle underlying adding an unsaturated phosphatecompound and a cyclic unsaturated carboxylic anhydride compound at thesame time is that during the first charging process, the unsaturatedphosphate compound forms a film on the anode, and the passivation filmformed by such compound on the anode has poor conductivity, which willsignificantly increase the impedance of the anode, resulting in thebattery having an significantly higher overall impedance and a poorlow-temperature performance; and the unsaturated cyclic carboxylicanhydride compound also has a very strong film-forming function on theanode during the first charging process, mainly in that such compoundhas a relatively higher film-forming potential on the anode and can takeprecedence over the unsaturated phosphate compound in forming a film onthe anode, thus suppressing subsequent film formation of the unsaturatedphosphate compound on the anode, and thereby decreasing batteryimpedance. In the present application, the unsaturated phosphatecompound and the unsaturated cyclic carboxylic anhydride compound areused together and work in synergy to produce special effects notachievable when either of them is used alone.

In light of the above description, the technical principle ofsimultaneously adding an unsaturated phosphate compound and a cyclicunsaturated carboxylic anhydride compound can be illustrated by FIG. 1and FIG. 2, wherein “Blank” in the figures is a blank electrolyte:EC/EMC/DEC=1/1/1 (volume ratio), LiPF6: 1M. It can be seen from FIG. 1and FIG. 2 that the unsaturated phosphate (Compound 1) starts filmformation on the anode at about 2.7 V during the first charging process,which film formation on the anode will result in significantly increasedimpedance of the anode; and when the cyclic unsaturated carboxylicanhydride compound (CA) is added in addition to the unsaturatedphosphate (Compound 1), the cyclic unsaturated carboxylic anhydridecompound (CA) will preferentially forms a film on the surface of theanode at about 1.5 V and 2 V, and the film preferentially formed by thecyclic unsaturated carboxylic anhydride compound (CA) will suppress thesubsequent film formation of the unsaturated phosphate (Compound 1) at2.7 V, thus lowering the impedance of the anode.

Specifically, the unsaturated phosphate compound represented by theabove Formula 1 may be selected from the group consisting of thecompounds of the following structural formulas

It is appreciated that both the unsaturated phosphate compoundrepresented by Formula 1 and the unsaturated phosphate compoundrepresented by Compound 1 to Compound 6 are preferred technicalsolutions of the present application, without the exclusion of othersaturated phosphate compounds having similar physical and chemicalproperties.

Specifically, the cyclic unsaturated carboxylic anhydride represented bythe above Formula 2 may be one or more selected from the groupconsisting of maleic anhydride (abbreviated as MA) and 2-methylmaleicanhydride (abbreviated as CA)

It is appreciated that the cyclic unsaturated carboxylic anhydridecompound represented by the above Formula 2, the MA and the CA are allpreferred technical solutions of the present application, without theexclusion of other cyclic unsaturated carboxylic anhydride compoundshaving similar physical and chemical properties.

Preferably, in the non-aqueous electrolyte for lithium-ion batteryaccording to the present application, the unsaturated phosphate compoundaccounts for 0.1% to 3%, more preferably 0.1% to 2% of the total weightof the non-aqueous electrolyte for lithium-ion battery.

It can be seen from the above description that when the content of theunsaturated phosphate compound is less than 0.1%, the film formingeffect on the cathode is deteriorated, the protective effect on thecathode is lowered, and the effect of improving the performances islowered; and when the content is more than 2%, the film formation at theelectrode interface tends to be thick, which increases the electrodeinterface impedance, especially the anode interface impedance, thusincreasing the overall impedance of the battery and deteriorating thebattery performances.

Preferably, in the non-aqueous electrolyte for lithium-ion batteryaccording to the present application, the cyclic unsaturated carboxylicanhydride compound accounts for 0.1% to 3%, more preferably 0.1% to 2%of the total weight of the non-aqueous electrolyte for lithium-ionbattery.

Also, it is understood from the above description that when the contentof the unsaturated cyclic carboxylic anhydride compound is less than0.1%, the film forming effect on the anode is deteriorated, and it isdifficult to effectively prevent the unsaturated phosphate compound fromforming a film on the anode; and when the content of the cycliccarboxylic anhydride compound is more than 2%, the film formation at theelectrode interface also tends to be thick, which increases theelectrode interface impedance, especially the anode interface impedance,thus increasing the overall impedance of the battery and deterioratingthe battery performances.

Further, the non-aqueous electrolyte for lithium-ion battery accordingto the present application further comprises at least one selected fromthe group consisting of an unsaturated cyclic carbonate or a cyclicsultone or a cyclic sulfate.

Further, the unsaturated cyclic carbonate compound accounts for 0.1% to5% of the total weight of the non-aqueous electrolyte, the cyclicsultone compound accounts for 0.1% to 5% of the total weight of thenon-aqueous electrolyte, and the cyclic sulfate compound accounts for0.1% to 5% of the total weight of the non-aqueous electrolyte.

Further, the unsaturated cyclic carbonate is at least one selected fromthe group consisting of vinylene carbonate and vinylethylene carbonate.

The cyclic sultone is at least one selected from the group consisting of1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone andmethylene methanedisulfonate.

The cyclic sulfate is one or both selected from the group consisting ofvinyl sulfate and propylene sulfate

The non-aqueous electrolyte of the present application comprises anon-aqueous organic solvent, the organic solvent being at least oneselected from the group consisting of ethylene carbonate, propylenecarbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,methyl ethyl carbonate and methyl propylene carbonate.

Further, in the non-aqueous electrolyte of the present application, thelithium salt is at least one selected from the group consisting oflithium hexafluorophosphate, lithium tetrafluoroborate, lithiumbis(trifluoromethylsulfonyl)imide, and lithium bisfluorosulfonimide.

Another aspect of the present application discloses a lithium-ionbattery, comprising a cathode, an anode, a separator interposed betweenthe cathode and the anode, and an electrolyte, wherein the electrolyteis the non-aqueous electrolyte for lithium-ion battery according to thepresent application.

The lithium-ion battery of the present application has a charge cut-offvoltage of greater than or equal to 4.3 V.

Further, in the lithium-ion battery of the present application, thecathode is at least one selected from the group consisting of LiCoO₂,LiNiO₂, LiMn₂O₄, LiCo_(1-y)M_(y)O₂, LiNi_(1-y)M_(y)O₂, LiMn_(2-y)M_(y)O₄and LiNi_(x)Co_(y)Mn_(z)M_(1-x-y-z)O₂; wherein M is at least oneselected from the group consisting of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al,Sn, B, Ga, Cr, Sr, V, and Ti, and 0≤y≤1, 0≤x≤1, 0≤z≤1, and x+y+z≤1.

It should be noted that the non-aqueous electrolyte of the presentapplication can be used in various lithium-ion batteries, including butnot limited to the types listed in the present application.

Technical Solution II:

At present, lithium-ion battery electrolytes use carbonate as a solvent.When the charging voltage of the lithium-ion battery is greater than4.2V, the carbonate solvent is oxidized and decomposes on the surface ofthe cathode material to generate gas and other decomposition products.On the one hand, the gas generated will cause the battery to bulge,which poses safety hazard to the battery. On the other hand, thedecomposition products will obviously increase the impedance of thebattery, thereby degrading the performances of the battery. Therefore,for a high-voltage lithium-ion battery, it is necessary to develop asolvent having a higher oxidation potential than the carbonate.According to literature report (Electrochemistry Communications 44(2014) 34-37), fluorocarbonate can significantly improve thehigh-temperature cycling performance of high-voltage lithium-ionbatteries. However, the present Applicant has found that althoughfluorocarbonate can improve the high-temperature cycling performance,gas production in the battery is serious during high-temperaturestorage, which poses a safety hazard. Chinese Patent Application No.CN104704657A discloses an electrolyte comprising a fluorinatedcarboxylate, which can improve the high-temperature cycling performanceof the high-voltage lithium-ion battery. Nevertheless, the presentApplicant has found that the fluorinated carboxylate has poorcompatibility with the carbon anode material, and will be reduced anddecompose to generate a large amount of gas on the surface of the anodeduring the charging process of the battery, which poses a great safetyhazard to the battery and significantly degrades the performances of thebattery. Chinese Patent No. 201410534841.0 discloses a triplebond-containing phosphate compound as a novel film-forming additive,which not only improves the high-temperature cycling performance, butalso significantly improves the storage performance. However,researchers in the art have found during researches that the passivationfilm formed by the triple bond-containing phosphate additive at theelectrode interface has poor conductivity, resulting in high interfaceimpedance, significantly degrading the low-temperature performance, andrestricting the application of the lithium-ion batteries containingnon-aqueous electrolyte under low temperature conditions. Patentliterature reports that cyclic carboxylic anhydrides can improve thehigh-temperature storage performance. However, the present inventorshave found that in an electrolyte with carbonate as a solvent, cycliccarboxylic anhydrides significantly increase the impedance of thebattery and degrade the low-temperature discharge performance and therate performance of the battery.

In this regard, an aspect of the present application discloses anon-aqueous electrolyte for lithium-ion battery, comprising Component Aand Component B; wherein Component A includes at least one selected fromthe group consisting of the fluorinated cyclic carbonates represented byStructural Formula 1, and also includes at least one selected from thegroup consisting of the alkyl-substituted cyclic carbonates representedby Structural Formula 2 and/or at least one selected from the groupconsisting of the fluorinated carboxylates represented by StructuralFormula 3;

wherein R₁ is a fluorine element or a fluorine-containing hydrocarbongroup having 1 to 4 carbon atoms, and R₂, R₃ and R₄ are eachindependently selected from a hydrogen element, a fluorine element, ahydrocarbon group having 1 to 4 carbon atoms or a fluorine-containinghydrocarbon group having 1 to 4 carbon atoms;

wherein R₅ is a hydrocarbon group having 1 to 4 carbon atoms, and R₆, R₇and R₈ are each independently selected from a hydrogen element or ahydrocarbon group having 1 to 4 carbon atoms;R₉COOR₁₀,  Structural Formula 3

wherein R₉ and R₁₀ are each independently selected from a hydrocarbongroup having 1 to 4 carbon atoms or a fluorohydrocarbon group having 1to 4 carbon atoms, and at least one of R₉ and R₁₀ is thefluorohydrocarbon group; and the fluorohydrocarbon group contains atleast two fluorine atoms;

wherein R₁₁ is an unsaturated hydrocarbon group having 1 to 4 carbonatoms, and R₁₂ and R₁₃ are each independently selected from a saturatedhydrocarbon group having 1 to 4 carbon atoms, an unsaturated hydrocarbongroup having 1 to 4 carbon atoms or a fluorohydrocarbon group having 1to 4 carbon atoms;

wherein R₁₄ is selected from the group consisting of an alkylene groupor alkenylene group having 2 to 4 carbon atoms, or a fluorine-containingalkylene group or fluorine-containing alkenylene group having 2 to 4carbon atoms.

It should be noted that the key of the non-aqueous electrolyte of thepresent application lies in that Component A and Component B are used incombination and work in synergy. The fluorocarbonate and thefluorocarboxylate in Component A can increase the oxidativedecomposition potential of the electrolyte, because the oxidationresistance of the fluorocarbonate and the fluorocarboxylate is higherthan that of the carbonate. Further, the fluorocarbonate and thefluorocarboxylate can form a passivation film on the surface of theanode, thereby suppressing the decomposition reaction of theelectrolyte. However, with regard to the fluorocarbonate solvent, duringhigh-temperature storage of the battery, the thermal stability of thepassivation film is not ideal, and a large amount of gas is generated,which lowers the high-temperature storage performance of the battery.With regard to the fluorocarboxylate solvent, it will decompose on thesurface of the anode to produce a large amount of gas during the firstcharging of the battery, resulting in poor contact between the electrodeplates, thereby degrading the performances of the battery. Although theunsaturated phosphate or cyclic carboxylic anhydride of Component B canform a passivation film on the surface of the cathode and the anode, theinternal resistance of the battery is remarkably increased, and thelow-temperature performance of the battery is remarkably lowered. WhenComponent A and Component B are used at the same time in the presentapplication, while Component A undergoes a film-forming reaction on thesurface of the cathode and the anode, Component B also participates inthe film-forming reaction on the cathode and the anode, such that thecomponents of the passivation layers on the cathode and the anodeincludes both the decomposition products of Component A and thedecomposition products of Component B, which improves the interfaces ofthe cathode and the anode. This not only improves the thermal stabilityof the passivation film on the anode, thus ensuring the high-temperatureperformance of the battery, but also will not significantly increase theimpedance of the battery, thus ensuring the low-temperature performanceof the battery. In the present application, Component A and Component Bare used together and work in synergy to produce special effects notachievable when either of them is used alone.

In the above electrolyte, Component A accounts for 10-90% of the totalweight of the non-aqueous electrolyte, and Component B accounts for0.1-3% of the total weight of the non-aqueous electrolyte.

In the present invention, the compound represented by Structural Formula1 is a necessary component and is used together with the substancerepresented by Structural Formula 2 and/or Structural Formula 3 as thesolvent. That is, according to the present invention, Component A may bea compound represented by Structural Formula 1 and a compoundrepresented by Structural Formula 2, or a compound represented byStructural Formula 1 and a compound of Structural Formula 3. Also, acompound represented by Structural Formula 1 and a compound representedby Structural Formula 2 and a compound represented by Structural Formula3 can be used together as Component A.

Preferably, the compound represented by Structural Formula 1 accountsfor 5% to 80% of the total weight of the non-aqueous electrolyte.

When the compound represented by Structural Formula 2 is present inComponent A, it is preferred that the compound represented by StructuralFormula 2 accounts for 5% to 80%, more preferably 5 to 30% of the totalweight of the non-aqueous electrolyte. When the compound represented byStructural Formula 3 is present in Component A, it is preferred that thecompound represented by Structural Formula 3 accounts for 5% to 80%,more preferably 20 to 70% of the total weight of the non-aqueouselectrolyte.

In the present invention, Component B is the compound represented byStructural Formula 4 and/or the compound represented by Structuralformula 5. When the compound represented by Structural Formula 4 ispresent in Component B, it is preferred that the compound represented byStructural Formula 4 accounts for 0.1% to 3% of the total weight of thenon-aqueous electrolyte. When the compound represented by StructuralFormula 5 is present in Component B, it is preferred that the compoundrepresented by Structural Formula 5 accounts for 0.1% to 3% of the totalweight of the non-aqueous electrolyte.

Preferably, the unsaturated cyclic carbonate is at least one selectedfrom the group consisting of vinylene carbonate and vinylethylenecarbonate.

Preferably, the compound represented by Structural Formula 1 is afluorinated cyclic carbonate. Preferably, the compound represented byStructural Formula 1 is one or more selected from the group consistingof the compounds of the following structural formulas:

Preferably, the compound represented by Structural Formula 2 is analkyl-substituted cyclic carbonate. Preferably, the compound representedby Structural Formula 2 is one or more selected from the groupconsisting of the compounds of the following structural formulas:

Preferably, in Structural Formula 3, the hydrocarbon group having 1 to 5carbon atoms is selected from the group consisting of methyl, ethyl,propyl, and butyl group; and the fluorohydrocarbon group is selectedfrom the group consisting of fluoromethyl, fluoroethyl, fluoropropyl,and fluorobutyl group.

Preferably, the fluorocarboxylate compound represented by StructuralFormula 3 is one or more selected from the group consisting ofH₃CCOOCH₂CF₂H (3-1, abbreviated as DFEA), H₃CH₂CCOOCH₂CF₂H (3-2,abbreviated as DFEP), HF₂CH₂CCOOCH₃ (3-3, abbreviated as MDFP),HF₂CH₂CCOOCH₂CH₃ (3-4, abbreviated as EDFP), HF₂CH₂CH₂CCOOCH₂CH₃ (3-5,abbreviated as EDFB), H₃CCOOCH₂CH₂CF₂H (3-6, abbreviated as DFPA),H₃CH₂CCOOCH₂CH₂CF₂H (3-7, abbreviated as DFPP), CH₃COOCH₂CF₃ (3-8,abbreviated as TFEA), HCOOCH₂CHF₂ (3-9, abbreviated as DFEF),HCOOCH₂CF₃, CH₃COOCH₂CF₂CF₂H (3-10, abbreviated as TFPA).

Preferably, the saturated hydrocarbon group having 1 to 4 carbon atomsin Structural Formula 4 includes, but is not limited to, methyl, ethyl,and propyl group; the unsaturated hydrocarbon group having 1 to 4 carbonatoms includes, but is not limited to, vinyl, allyl, 3-butenyl,isobutenyl, ethynyl, propargyl, 3-butynyl, and 1-methyl-2-propynylgroup; and the halohydrocarbon group includes, but is not limited todifluoromethyl, trifluoromethyl, 2,2-difluoroethyl,2,2,2-trifluoroethyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl, andhexafluoroisopropyl group.

Preferably, the unsaturated phosphate compound represented by StructuralFormula 4 is one or more selected from the group consisting oftripropargyl phosphate (4-1), dipropargyl methyl phosphate (4-2),dipropargylethyl phosphate (4-3), dipropargylpropyl phosphate (4-4),dipropargyl trifluoromethyl phosphate (4-5), dipropargyl2,2,2-trifluoroethyl phosphate (4-6), dipropargyl 3,3,3-trifluoropropylphosphate (4-7), dipropargyl hexafluoroisopropyl phosphate (4-8),triallyl phosphate (4-9), diallyl methyl phosphate (4-10), diallyl ethylphosphate (4-11), diallyl propyl phosphate (4-12), diallyltrifluoromethyl phosphate (4-13), diallyl 2,2,2-trifluoroethyl phosphate(4-14), diallyl 3,3,3-trifluoropropyl phosphate (4-15) and diallylhexafluoroisopropyl phosphate (4-16).

Preferably, the cyclic carboxylic anhydride represented by StructuralFormula 5 is one or more selected from the group consisting of succinicanhydride (5-1, abbreviated as SA), maleic anhydride (5-2, abbreviatedas MA), 2-methylmaleic anhydride (5-3, abbreviated as CA).

Preferably, the non-aqueous electrolyte further comprises at least oneselected from the group consisting of an unsaturated cyclic carbonate, acyclic sultone, and a cyclic sulfate.

Preferably, the unsaturated cyclic carbonate compound accounts for 0.1%to 5% of the total weight of the non-aqueous electrolyte, the cyclicsultone compound accounts for 0.1% to 5% of the total weight of thenon-aqueous electrolyte, and the cyclic sulfate compound accounts for0.1% to 5% of the total weight of the non-aqueous electrolyte.

Preferably, the unsaturated cyclic carbonate is at least one selectedfrom the group consisting of vinylene carbonate and vinylethylenecarbonate.

Preferably, the cyclic sulfate is at least one selected from the groupconsisting of:

Preferably, the cyclic sultone is at least one selected from the groupconsisting of 1,3-propane sultone (abbreviated as PS), 1,4-butanesultone (abbreviated as BS), and 1,3-propene sultone (abbreviated asPST), methylene methanedisulfonate (abbreviated as MMDS).

Preferably, the non-aqueous electrolyte further comprises at least oneselected from the group consisting of ethylene carbonate, propylenecarbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,methyl ethyl carbonate, and methyl propyl carbonate. The content thereofmay vary within a wide range, and preferably, the content thereofaccounts for 1% to 40% of the total weight of the non-aqueouselectrolyte. It is appreciated that when a plurality of the abovesubstances are present, the above content range refers to that for thetotal content of the plurality of the above substances.

Another aspect of the present application discloses a lithium-ionbattery, comprising a cathode, an anode, a separator interposed betweenthe cathode and the anode, and an electrolyte, wherein the electrolyteis the non-aqueous electrolyte for lithium-ion battery according to thepresent application.

Preferably, the cathode active material is at least one selected fromthe group consisting of LiNi_(x)Co_(y)Mn_(z)L_((1-x-y-z))O₂,LiCo_(x′)L_((1-x′))O₂ and LiNi_(x″)L′_(y′)Mn_((2-x″-y′))O₄, wherein L isAl, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<x+y+z≤1,0<x′≤1, 0.3≤x″≤0.6, and 0.01≤y′≤0.2, and L′ is Co, Al, Sr, Mg, Ti, Ca,Zr, Zn, Si or Fe.

Technical Solution III:

At present, lithium-ion battery electrolytes use carbonate as a solvent.When the charging voltage of the lithium-ion battery is greater than4.2V, the carbonate solvent is oxidized and decomposes on the surface ofthe cathode material to generate gas and other decomposition products.On the one hand, the gas generated will cause the battery to bulge,which poses safety hazard to the battery. On the other hand, thedecomposition products will obviously increase the impedance of thebattery, thereby degrading the performances of the battery. Therefore,for a high-voltage lithium-ion battery, it is necessary to develop asolvent having a higher oxidation potential than the carbonate. ChinesePatent Application No. CN104704657A discloses an electrolyte comprisinga fluorinated carboxylate and a phosphate, which can improve thehigh-temperature cycling performance of the high-voltage lithium-ionbattery. Nevertheless, the present Applicant has found that thefluorinated carboxylate has poor compatibility with the carbon anodematerial, and will be reduced and decompose to generate a large amountof gas on the surface of the anode during the charging process of thebattery, which poses a great safety hazard to the battery andsignificantly degrades the performances of the battery. Although thephosphate can inhibit the decomposition of the fluorocarboxylate to acertain extent, the high-temperature cycling and high-temperaturestorage performance need to be further improved.

In this regard, another aspect of the present application discloses anon-aqueous electrolyte for lithium-ion battery, comprising at least oneselected from the group consisting of a first compounds represented byStructural Formula 3 and at least one selected from the group consistingof a second compounds represented by Structural Formula 4;

Structural Formula 3: R₉COOR₁₀, wherein R₉ and R₁₀ are eachindependently selected from a hydrocarbon group or a fluorinatedhydrocarbon group having 1 to 5 carbon atoms, and at least one of R₉ andR₁₀ is the fluorinated hydrocarbon group; and the fluorinatedhydrocarbon group has at least two hydrogen atoms substituted byfluorine;

wherein R₁₁, R₁₂ and R₁₃ are each independently selected from asaturated hydrocarbon group, an unsaturated hydrocarbon group or ahalogenated hydrocarbon group having 1 to 5 carbon atoms, and at leastone of R₁₁, R₁₂ and R₁₃ is an unsaturated hydrocarbon group.

It should be noted that the key of the non-aqueous electrolyte of thepresent application lies in that the first compounds represented byStructural Formula 3 and the second compounds represented by StructuralFormula 4 are used in combination and work in synergy. The firstcompounds, due to the high oxidation potential, can reduce thedecomposition reaction of the electrolyte on the surface of thehigh-voltage cathode material, but the first compounds will decompose onthe surface of the anode, thereby generating a large amount of gas,which poses a safety hazard. The second compounds, due to theunsaturated bond present in the molecular structure, can undergo apolymerization reaction on the material surface of the cathode and theanode to form a passivation film during the initial charging process ofthe lithium-ion battery, but the passivation film has a high impedance,which lowers the low-temperature discharge performance and the rateperformance of the battery. When the first compounds and the secondcompounds are used together in the present application, the secondcompounds preferentially undergo a polymerization reaction to form apassivation film on the surface of the anode, which can inhibit thedecomposition reaction of the first compounds on the surface of theanode, thereby suppressing gas generation from decomposition of thefirst compounds on the surface of the anode during the charging process.In addition, the first compounds can also partially participate in thefilm-forming reaction on the anode, thereby improving the interface ofthe anode. The first compounds and the second compounds are usedtogether and work in synergy to produce special effects not achievablewhen either of them is used alone.

In the present application, the first compounds and the second compoundsare used together; wherein the first compounds can be added in aconventional amount, for example, preferably, the first compoundsaccount for 10% to 80% of the total weight of the non-aqueouselectrolyte; the second compound may be used in an amount according tothe conventional amounts of the additives for non-aqueous electrolytes,for example, about 0.8-1.2% of the total weight of the non-aqueouselectrolyte, or generally, 0.01%-5% of the total weight of thenon-aqueous electrolyte. The first compounds may be used alone as anon-aqueous organic solvent for the non-aqueous electrolyte, or may beused in combination with other common organic solvents, which will bedescribed in detail hereinafter.

It should also be noted that the key to the present application lies inthe use of the first compounds and the second compounds in thenon-aqueous electrolyte. As for other conventional components, such aslithium salts, reference may be made to existing non-aqueouselectrolytes, and further, other commonly used reagents may be added tothe non-aqueous electrolyte to enhance the corresponding functions,which are not specifically limited herein. However, in the preferredembodiments of the present application, in order to achieve a bettereffect, other organic solvents than the non-aqueous organic solvent,lithium salts and other reagents are specifically defined, which will bedescribed in detail hereinafter.

Preferably, in the Structural Formula 1, the hydrocarbon group having 1to 5 carbon atoms includes, but is not limited to, methyl, ethyl,propyl, vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl,propargyl, 3-butynyl, 1-methyl-2-propynyl; and the fluorohydrocarbongroup includes, but is not limited to, difluoromethyl, trifluoromethyl,2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl,3,3,3-trifluoropropyl, and hexafluoroisopropyl;

In Structural Formula 2, the saturated hydrocarbon group having 1 to 5carbon atoms includes, but is not limited to, methyl, ethyl, and propylgroup; the unsaturated hydrocarbon group having 1 to 5 carbon atomsincludes, but is not limited to, vinyl, allyl, 3-butenyl, isobutenyl,4-pentenyl, ethynyl, propargyl, 3-butynyl, 1-methyl-2-propynyl group;and the halogenated hydrocarbon group having 1 to 5 carbon atomsincludes, but is not limited to, difluoromethyl, trifluoromethyl,2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl,3,3,3-trifluoropropyl, and hexafluoroisopropyl group.

Preferably, the first compounds are selected from H₃CCOOCH₂CF₂H (3-1,abbreviated as DFEA), H₃CH₂CCOOCH₂CF₂H (3-2, abbreviated as DFEP),HF₂CH₂CCOOCH₃ (3-3, abbreviated as MDFP), HF₂CH₂CCOOCH₂CH₃ (3-4,abbreviated as EDFP), HF₂CH₂CH₂CCOOCH₂CH₃ (3-5, abbreviated as EDFB),H₃CCOOCH₂CH₂CF₂H (3-6, abbreviated as DFPA), H₃CH₂CCOOCH₂CH₂CF₂H (3-7,abbreviated as DFPP), CH₃COOCH₂CF₃ (3-8, abbreviated as TFEA),HCOOCH₂CHF₂ (3-9, abbreviated as DFEF), HCOOCH₂CF₃, CH₃COOCH₂CF₂CF₂H(3-10, abbreviated as TFPA).

Preferably, the second compounds are at least one selected from thegroup consisting of tripropargyl phosphate, dipropargyl methylphosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate,dipropargyl trifluoromethyl phosphate, dipropargyl 2,2,2-trifluoroethylphosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, dipropargylhexafluoroisopropyl phosphate, triallyl phosphate, diallyl methylphosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyltrifluoromethyl phosphate, diallyl 2,2,2-trifluoroethyl phosphate,diallyl 3,3,3-trifluoropropyl phosphate or diallyl hexafluoroisopropylphosphate.

Preferably, the non-aqueous electrolyte further comprises one or moreselected from the group consisting of an unsaturated cyclic carbonate,an unsaturated acid anhydride, a cyclic sulfate, a cyclic sultone and asulfone.

The unsaturated cyclic carbonate includes at least one selected from thegroup consisting of vinylene carbonate (abbreviated as VC) andvinylethylene carbonate (abbreviated as VEC);

Preferably, the cyclic sultone includes at least one selected from thegroup consisting of 1,3-propane sultone (abbreviated as 1,3-PS),1,4-butane sultone (abbreviated as BS), 1,3-propene sulfone (abbreviatedas PST) and methylene methanedisulfonate (abbreviated MMDS).

Preferably, the unsaturated acid anhydride includes at least oneselected from the group consisting of succinic anhydride (abbreviated asSA), maleic anhydride (abbreviated as MA), and 2-methylmaleic anhydride(CA).

Preferably, the cyclic sulfate comprises one or both selected from thegroup consisting of vinyl sulfate (abbreviated as DTD) and propylenesulfate (abbreviated as TS).

Preferably, the sulfone includes sulfolane (abbreviated as SL).

It should be noted that vinylene carbonate (abbreviated as VC),vinylethylene carbonate (abbreviated as VEC), fluoroethylene carbonate(abbreviated FEC), or 1,3-propane sultone (abbreviated as 1,3PS),1,4-butane sultone (abbreviated as BS), 1,3-propene sultone (abbreviatedas PST), methylene methanedisulfonate (abbreviated as MMDS), succinicanhydride (abbreviated SA), maleic anhydride (abbreviated as MA),2-methylmaleic anhydride (abbreviated as CA), vinyl sulfate (abbreviatedDTD), propylene sulfate (abbreviated as TS), sulfolane (abbreviated asSL) and 1,4-butyrolactone (abbreviated as GBL) are all conventionalreagents reported for non-aqueous electrolytes. Some of these reagentscan be used as an additive or as a solvent, such as FEC, which can beregarded as an solvent when used in a relatively large amount, and canbe regarded as an additive when used in a relatively small amount. Forexample, in the present invention, preferably, VC accounts for 0.1% to4%, more preferably 0.5% to 1.5% of the total weight of the non-aqueouselectrolyte; VEC accounts for 0.1% to 3%, more preferably 0.2% to 1.5%of the total weight of the non-aqueous electrolyte; 1,3-PS accounts for0.1% to 10%, more preferably 1% to 3% of the total weight of thenon-aqueous electrolyte; BS accounts for 0.1% to 10%, more preferably 1%to 3% of the total weight of the non-aqueous electrolyte; PST accountsfor 0.1% to 3%, more preferably 0.5% to 2% of the total weight of thenon-aqueous electrolyte; MMDS accounts for 0.1% to 4%, more preferably0.5% to 2% of the total weight of the non-aqueous electrolyte; SAaccounts for 0.1% to 4%, more preferably 0.5% to 2% of the total weightof the non-aqueous electrolyte; MA accounts for 0.1% to 4%, morepreferably 0.5% to 2% of the total weight of the non-aqueouselectrolyte; CA accounts for 0.1% to 4%, more preferably 0.5% to 2% ofthe total weight of the non-aqueous electrolyte; DTD accounts for 0.1%to 5%, more preferably 0.5% to 3% of the total weight of the non-aqueouselectrolyte; TS accounts for 0.1% to 4%, more preferably 0.5% to 3% ofthe total weight of the non-aqueous electrolyte; SL accounts for 0.1% to30%, more preferably 2 to 15% of the total weight of the non-aqueouselectrolyte; and GBL accounts for 0.1% to 30%, more preferably 2 to 15%of the total weight of the non-aqueous electrolyte.

Preferably, the non-aqueous electrolyte further comprises at least oneselected from the group consisting of ethylene carbonate, fluoroethylenecarbonate (abbreviated as FEC), propylene carbonate, butylene carbonate,dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, andmethyl propyl carbonate. The content thereof may vary within a widerange, and preferably, the content thereof accounts for 1% to 40% of thetotal weight of the non-aqueous electrolyte. It is appreciated that whena plurality of the above substances are present, the above content rangerefers to that for the total content of the plurality of the abovesubstances.

More preferably, the non-aqueous electrolyte further comprises at leastone selected from the group consisting of ethylene carbonate,fluoroethylene carbonate and propylene carbonate.

Another aspect of the present application discloses a use of thenon-aqueous electrolyte of the present application in a lithium-ionbattery or a storage capacitor.

Another aspect of the present application discloses a lithium-ionbattery, comprising a cathode, an anode, a separator interposed betweenthe cathode and the anode, and an electrolyte, wherein the electrolyteis the non-aqueous electrolyte for lithium-ion battery according to thepresent application.

It is appreciated that the key of the lithium-ion battery of the presentapplication lies in the use of the non-aqueous electrolyte of thepresent application, so that a passivation film is formed on the surfaceof the cathode and the anode, thereby effectively inhibiting thedecomposition reaction of the electrolyte on the surface of the cathodeand the anode, suppressing the destruction of the structure of thecathode material, reducing lithium precipitation, thus ensuring thehigh- and low-temperature performances and the rate performance of thebattery. As for other components in the lithium-ion battery, such as thecathode, the anode and the separator, reference may be made toconventional lithium-ion batteries. In preferred embodiments of thepresent application, the cathode active material is specificallydefined.

Preferably, the cathode active material is at least one selected fromthe group consisting of LiNi_(x)Co_(y)Mn_(z)L_((1-x-y-z))O₂,LiCo_(x′)L_((1-x′))O₂ and LiNi_(x″)L′_(y′)Mn_((2-x″-y′))O₄, wherein L isAl, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<x+y+z≤1,0<x′≤1, 0.3≤x″≤0.6, and 0.01≤y′≤0.2, and L′ is Co, Al, Sr, Mg, Ti, Ca,Zr, Zn, Si or Fe.

Due to the adoption of the above technical solutions, the presentapplication has the following beneficial effects:

In the non-aqueous electrolyte of the present application, the firstcompounds represented by Structural Formula 1 and the second compoundsrepresented by Structural Formula 2 are used in combination and work insynergy, which not only improves the high-temperature cyclingperformance of the high-voltage lithium-ion battery, but also avoids gasgeneration due to decomposition on the surface of the anode. Moreover,the first compounds can also partially participate in the film formingreaction on the anode, thereby improving the interface of the anode andensuring the low-temperature discharge performance and the rateperformance of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a capacity differential graph for the initial charging of ablank electrolyte, Example 6 and Comparative Example 1; and

FIG. 2 is an alternating current impedance graph of a blank electrolyte,Example 6 and Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

The present application will be further described in detail below byreference to particular examples and the accompanying drawings. Thefollowing examples are only intended to further illustrate theapplication and are not to be construed as limiting the invention.

EXAMPLES

Technical Solution I:

In this technical solution, electrolytes were prepared according to thecomponents and ratios shown in Table 1. A plurality of non-aqueouselectrolytes for lithium-ion battery according to the presentapplication as well as a plurality of Comparative Examples weredesigned, as shown in Table 1 in detail.

In this technical solution, lithium hexafluorophosphate was used as thelithium salt. It is appreciated that the lithium salt used in thistechnical solution served only as a particular embodiment. Other lithiumsalts used in the art, such as LiBF₄, LiBOB, LiDFOB, LiPO₂F₂, LiSbF₆,LiAsF₆, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiC(SO₂CF₃)₃ and LiN(SO₂F)₂, canalso be used in this technical solution, and are not specificallylimited herein.

The electrolytes in this technical solution were prepared by preparing anon-aqueous organic solvent according to a volume ratio ofEC/EMC/DEC=1/1/1 (volume ratio), and then adding lithiumhexafluorophosphate to the solvent to a final concentration of 1.0mol/L, and then adding the additive according to Table 1. The percentagein Table 1 was percentage by weight, i.e., the percentage of theadditive based on the total weight of the electrolyte.

TABLE 1 The components and their contents in the electrolytesUnsaturated cyclic carboxylic anhydride Other and additive Unsaturatedphosphate content and content Example compound thereof thereof Example 1Tripropargyl phosphate: 0.5% CA: 0.1% Example 2 Tripropargyl phosphate:0.5% CA: 0.5% Example 3 Tripropargyl phosphate: 0.5% CA: 1% Example 4Tripropargyl phosphate: 0.5% CA: 2% Example 5 Tripropargyl phosphate:0.1% CA: 0.5% Example 6 Tripropargyl phosphate: 1% CA: 0.5% Example 7Tripropargyl phosphate: 2% CA: 0.5% Example 8 Tripropargyl phosphate: 1%CA: 0.1% Example 9 Tripropargyl phosphate: 0.1% CA: 1% Example 10Tripropargyl phosphate: 0.5% MA: 0.5% Example 11 Tripropargyl phosphate:0.5% MA: 1% Example 12 Tripropargyl phosphate: 0.5% CA: 0.5% Vinylenecarbonate: 1% Example 13 Tripropargyl phosphate: 0.5% CA: 0.5%1,3-propane sultone: 1% Example 14 Tripropargyl phosphate: 0.5% CA: 0.5%Vinyl sulfate: 1% Example 15 Diallylethyl phosphate: 0.5% CA: 0.5%Example 16 Diallylethyl phosphate: 1% CA: 0.5% Example 17 Diallylethylphosphate: 2% CA: 0.5% Example 18 Diallylethyl phosphate: 1% CA: 0.1%Comparative Tripropargyl phosphate: 1% Example 1 ComparativeDiallylethyl phosphate: 1% Example 2

In the lithium-ion batteries in this technical solution, the cathodeactive material used was LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂, the anode usedwas artificial graphite, and the separator used was a three-layerseparator of polypropylene, polyethylene and polypropylene.Specifically, lithium-ion batteries were made as follows.

Preparation of the cathode: Cathode active materialLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂, conductive carbon black and binderpolyvinylidene fluoride were mixed in a mass ratio of 96.8:2.0:1.2. Themixture was dispersed in N-methyl-2-pyrrolidone to obtain a cathodeslurry. The cathode slurry was uniformly coated onto both sides of analuminum foil, which was then subjected to oven drying, calandering andvacuum drying, followed by welding of aluminum lead wires by anultrasonic welder to obtain the cathode plate, the thickness of theplate being in the range of 120-150 μm.

Preparation of the anode: Graphite, conductive carbon black and bindersstyrene-butadiene rubber and carboxymethyl cellulose were mixed in amass ratio of 96:1:1.2:1.8. The mixture was dispersed in deionized waterto obtain an anode slurry. The anode slurry was coated onto both sidesof a copper foil, which was then subjected to oven drying, calanderingand oven drying, followed by welding of nickel lead wires by anultrasonic welder to obtain the anode plate, the thickness of the platebeing in the range of 120-150 μm.

Preparation of the separator: a three-layer separator of polypropylene,polyethylene and polypropylene was used, the thickness being 20 μm.

Battery assembling: the three-layer separator having a thickness of 20μm was placed between the cathode plate and the anode plate, and theresulting sandwich structure composed of the cathode plate, the anodeplate and the separator was wound. The wound structure was flattened andplaced into an aluminum foil packing bag, and baked at 75° C. for 48hours to obtain a battery core, which was to be injected withelectrolyte. Then, the battery core was injected with an electrolyteprepared as above, and was vacuum-packed and allowed to stand for 24hours.

Battery formation: 0.05C constant current charging for 180 min, 0.1Cconstant current charging to 3.95V, vacuum packing again and standing at45° C. for 48 h, then further, 0.2C constant current charging to 4.4V,and 0.2C constant current discharging to 3.0V.

The batteries having the respective electrolytes in this technicalsolution were subjected to capacity retention rate test of 1C cyclingfor 300 cycles at 45° C. and 1C cycling for 500 cycles at normaltemperature; capacity retention rate, capacity recovery rate, andthickness expansion rate tests after storage at 60° C. for 30 days; 1Cdischarging efficiency test at −20° C.; and normal and low temperaturedirect current impedance test. The specific test methods are as follows:

(1) The capacity retention rate test of 1C cycling for 300 cycles at 45°C. was in fact to measure the high-temperature cycling performance ofthe battery. The specific test method comprised: subjecting, at 45° C.,the formed battery to 1C constant current and constant voltage chargingto 4.35V, with the cut-off current being 0.01C, followed by 1C constantcurrent discharging to 3.0V. After 300 cycles of charging/discharging,the capacity retention rate at the 300^(th) cycle was calculated toevaluate the high-temperature cycling performance. The formula forcalculating the capacity retention rate after 1C cycling for 300 cyclesat 45° C. is as follows:Capacity retention rate at the 300^(th) cycle (%)=(discharge capacity atthe 300^(th) cycle/discharge capacity at the 1^(st) cycle)×100%.

(2) Normal temperature cycling performance test: At 25° C., the formedbattery was subjected to 1C constant current constant voltage chargingto 4.35 V, then 1C constant current discharging to 3.0 V. The capacityretention rate at the 500^(th) cycle after 500 cycles ofcharging/discharging was calculated to evaluate the normal temperaturecycling performance. The formula for calculation is as follows:Capacity retention rate at the 500^(th) cycle (%)=(discharge capacity atthe 500^(th) cycle/discharge capacity at the 1^(st) cycle)×100%.

(3) The test method of capacity retention rate, capacity recovery rateand thickness expansion rate after storage at 60° C. for 30 dayscomprised: subjecting, at a normal temperature, the formed battery to 1Cconstant current constant voltage charging to 4.35 V, with the cut-offcurrent being 0.01C; followed by 1C constant current discharging to 3.0V, at which time the initial discharge capacity of the battery wasmeasured, followed by 1C constant current constant voltage charging to4.35V, with the cut-off current being 0.01C, at which time the initialthickness of the battery was measured; followed by storage of thebattery at 60° C. for 30 days, at which time the thickness of thebattery was measured; followed by 1C constant current discharging to3.0V, at which time the retention capacity of the battery was measured;followed by 1C constant current constant voltage charging to 4.35V, withthe cut-off current being 0.01C; and followed by 1C constant currentdischarging to 3.0 V, at which time the recovery capacity was measured.The formulas for calculating the capacity retention rate, capacityrecovery rate, and thickness expansion rate are as follows:Battery capacity retention rate (%)=retention capacity/initialcapacity×100%Battery capacity recovery rate (%)=recovery capacity/initialcapacity×100%Battery thickness expansion rate (%)=(thickness after 30 days−initialthickness)/initial thickness×100%.

(4) Low-temperature discharge performance test: At 25° C., the formedbattery was subjected to 1C constant current constant voltage chargingto 4.35 V, then 1C constant current discharging to 3.0 V, at which timethe discharge capacity was recorded. Then, the battery was subjected to1C constant current constant voltage charging to full capacity, allowedto stand in an environment of −20° C. for 12 hours, then subjected to 1Cconstant current discharging to 3.0 V, at which time the dischargecapacity was recorded.

Low-temperature discharge efficiency value at −20° C.=1C dischargecapacity (−20° C.)/1C discharge capacity (25° C.).

(5) Normal temperature direct current impedance (DCIR) performance test:Subjecting, at 25° C., the formed battery to 1C charging to SOC=50%,followed by respectively subjecting the battery to 0.1C, 0.2C, 0.5C, 1C,and 2C charging and discharging for 10 seconds and respectivelyrecording the charge and discharge cut-off voltage. Then, a linearrelationship plot (unit: mV) was prepared by plotting the charge anddischarge currents at different rates on the abscissa (unit: A) andplotting the cut-off voltages corresponding to the charge and dischargecurrents on the ordinate.

Discharge DCIR value=slope of the linear plot of different dischargecurrents vs corresponding cut-off voltages.

The test results are shown in Table 2.

TABLE 2 Test results Cycling capacity retention rate/% High-temperaturestorage 1 C 45° C. Normal performance (60° C., 30 days) discharge (1 C/1C, temperature Capacity Capacity Thickness efficiency 25° C. 300 (1 C/1C, retention recovery expansion at discharge Test item cycles) 500cycles) rate/% rate/% rate/% −20° C. DCIR/mΩ Comparative 72.1 82.8 73.578.9 13.5 40.3 145.6 Example 1 Comparative 70.2 80.1 70.3 74.6 15.5 39.3140.2 Example 2 Example 1 75.3 83.8 77.6 80.1 10.3 42.7 129.2 Example 282.2 85.6 81.3 85.2 5.8 47.6 126.7 Example 3 81.9 84.6 80.1 83.4 6.843.5 128.9 Example 4 81.1 83.4 80.2 83.9 7.5 42.3 131.2 Example 5 73.583.4 76.8 79.2 11.3 53.2 118.7 Example 6 84.3 83.6 85.3 88.3 3.8 45.3132.7 Example 7 85.5 83.8 85.9 88.6 5.3 43.2 135.3 Example 8 78.5 81.279.5 83.2 8.5 42.3 137.2 Example 9 72.5 73.5 73.5 79.2 14.8 48.7 125.3Example 10 80.2 81.3 78.9 84.2 8.8 45.5 125.8 Example 11 78.9 82.3 78.282.3 9.7 46.3 126.8 Example 12 83.3 87.5 83.2 84.5 7.8 45.6 127.8Example 13 80.2 82.3 80.3 83.5 5.2 47.2 125.3 Example 14 83.9 86.6 84.387.2 4.2 48.5 123.5 Example 15 80.1 84.6 78.3 81.3 6.8 45.5 127.2Example 16 83.3 82.4 82.3 85.3 4.2 44.2 129.6 Example 17 85.9 84.2 85.187.6 5.2 42.3 137.6 Example 18 76.5 81.9 76.5 79.2 10.5 40.3 136.2

Through the tests, an initial charging capacity differential plot (asshown in FIG. 1) and an AC impedance plot (as shown in FIG. 2) wereobtained for the blank electrolyte, Example 6 and Comparative Example 1.

It can be seen from FIG. 1 and FIG. 2 that the unsaturated phosphate(Compound 1) began to form a film on the anode at about 2.7 V during theinitial charging process, and the film formation on the anode at thistime caused a significant increase in the impedance of the anode. Whenthe cyclic unsaturated carboxylic anhydride compound (CA) was added onthe basis of the unsaturated phosphate (Compound 1), the cyclicunsaturated carboxylic anhydride compound (CA) preferentially formed afilm on the surface of the anode at about 1.5 V and 2 V, and the filmpreferentially formed by the cyclic unsaturated carboxylic anhydridecompound (CA) inhibited the film formation by the unsaturated phosphate(Compound 1) at the subsequent 2.7 V, thereby further lowering theimpedance of the anode.

By comparing the test results of Comparative Examples 1-2, it can befound that when the unsaturated phosphate compound was used alone, thecycling performance and the high-temperature storage were good, but theimpedance was high and the low-temperature performance was poor. Whenthe unsaturated cyclic carboxylic anhydride compound was used alone, theimpedance was low and the low-temperature performance was good, but thecycling performance and the high-temperature storage were poor.

Among the test results of Examples 1-18 of the present application, bycomparing Comparative Example 1 with Examples 2, 6, and 8, it can befound that addition of the unsaturated cyclic carboxylic anhydridecompound on the basis of the unsaturated phosphate compound not onlysignificantly improved the cycling performance and the high-temperatureperformance, but also significantly improved the low-temperatureperformance, and significantly lowered the impedance.

Also, among the test results of Examples 1 to 18 of the presentapplication, it can be found that relative to Comparative Example 1, allthe Examples containing both the unsaturated phosphate compound and theunsaturated cyclic carboxylic anhydride compound had improvedhigh-temperature performance and low-temperature performance. ComparingExamples 2, 5, 6 and 7, it can be found that as the content of theunsaturated phosphate compound increased, the high-temperatureperformance improved, but the low-temperature performance was relativelydegraded, and especially, as the content increased, the impedanceincreased accordingly. In particular, when the content of theunsaturated phosphate compound was very high and the content of theunsaturated cyclic carboxylic anhydride compound was very low, theimpedance was high and the low-temperature performance was obviouslyinsufficient.

In summary of the above, the present application used the unsaturatedphosphate compound and the unsaturated cyclic carboxylic anhydridecompound in combination, which, in suitable ratios, allowed the batteryto have excellent high-temperature performance and cycling performanceas well as good low-temperature performance.

Technical Solution II:

Electrolytes were prepared according to the components and ratios shownin Table 3. A plurality of non-aqueous electrolytes for lithium-ionbattery according to the present application as well as a plurality ofComparative Examples were designed, as shown in Table 3 in detail.

The electrolytes in this technical solution were prepared by preparing anon-aqueous organic solvent according to the volume ratio shown in Table3, and then adding lithium hexafluorophosphate to the solvent to a finalconcentration of 1.0 mol/L, and then adding the additive according toTable 3. The percentage in Table 3 was percentage by weight, i.e., thepercentage of the additive based on the total weight of the electrolyte.The lithium salt content of the electrolyte was 12.5%, and others weresolvent grade additives.

TABLE 3 The components and their contents in the electrolytes Totalcontent, composition and weight ratio of the solvent Additive and itscontent Example 19 Total content: 87% Tripropargyl phosphate: 0.5%FEC/PC/EC = 2/1/1 Example 20 Total content: 86.5% Tripropargylphosphate: 1% FEC/PC/DEC = 2/1/1 Example 21 Total content: 86.5%Hexafluoroisopropyl- FEC/PC/EMC = 2/1/1 dipropargyl phosphate: 1%Example 22 Total content: 86.5% Dipropargyl methyl FEC/PC/DEC/EC =2/1/1/1 phosphate: 1% Example 23 Total content: 86.5% MA: 1% FEC/DFEA =2/1 Example 24 Total content: 86.5% CA: 1% FEC/DFEA/EC = 2/1/1 Example25 Total content: 86.5% Tripropargyl phosphate: 0.5%, FEC/DFEA/DEC =2/1/1 CA: 0.5% Example 26 Total content: 86.5% Tripropargyl phosphate:0.5% FEC/PC/DEC = 2/1/1 VC: 0.5% Example 27 Total content: 86.5%Tripropargyl phosphate: 0.5% FEC/PC/DEC = 2/1/1 PS: 0.5% Example 28Total content: 85.5% Tripropargyl phosphate: 1% FEC/PC/DEC = 2/1/1 DTD:1% Example 29 Total content: 84.5% Tripropargyl phosphate: 1% FEC/PC/DEC= 2/1/1 DTD: 2% Example 30 Total content: 85.5% CA: 1% FEC/PC/DEC =2/1/1 DTD: 1% Example 31 Total content: 85% Tripropargyl phosphate: 1%FEC/PC/DEC = 2/1/1 CA: 0.5 DTD: 1% Example 32 Total content: 86.5%Tripropargyl phosphate: 0.5% FEC/DFEA = 2/1 CA: 0.5% Example 33 Totalcontent: 85.5% Tripropargyl phosphate: 1% FEC/DFEA = 2/1 DTD: 1% Example34 Total content: 85.5% CA: 1% FEC/DFEA = 2/1 DTD: 1% Example 35 Totalcontent: 85% Tripropargyl phosphate: 1% FEC/DFEA = 2/1 CA: 0.5 DTD: 1%Example 36 Total content: 86.5% Tripropargyl phosphate: 0.5% FEC/PC/DFEA= 2/1/1 CA: 0.5% Example 37 Total content: 84.5% Tripropargyl phosphate:1% FEC/PC/DFEA = 2/1/1 DTD: 2% Example 38 Total content: 85.5% CA: 1%FEC/PC/DFEA = 2/1/1 DTD: 1% Comparative Total content: 87.5% Example 3FEC/PC/DEC = 2/1/1 Comparative Total content: 87.5% Example 4 FEC/DFEA =2/1 Comparative Total content: 87.5% Example 5 FEC/PC/DFEA = 2/1/1Comparative Total content: 87.5% Example 6 EC/DEC = 2/1 ComparativeTotal content: 86.5% Tripropargyl phosphate: 1% Example 7 EC/DEC = 2/1Comparative Total content: 86.5% CA: 1% Example 8 EC/DEC = 2/1

In the lithium-ion batteries in this technical solution, the cathodeactive material used was LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂, the anode usedwas artificial graphite and conductive carbon black, and the separatorused was a three-layer separator of polypropylene, polyethylene andpolypropylene. Specifically, lithium-ion batteries were made as follows.

Preparation of the cathode: Cathode active materialLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂, conductive carbon black and binderpolyvinylidene fluoride were mixed in a mass ratio of 96.8:2.0:1.2. Themixture was dispersed in N-methyl-2-pyrrolidone to obtain a cathodeslurry. The cathode slurry was uniformly coated onto both sides of analuminum foil, which was then subjected to oven drying, calandering andvacuum drying, followed by welding of aluminum lead wires by anultrasonic welder to obtain the cathode plate, the thickness of theplate being in the range of 120-150 μm.

Preparation of the anode: Graphite, conductive carbon black and bindersstyrene-butadiene rubber and carboxymethyl cellulose were mixed in amass ratio of 96:1:1.2:1.8. The mixture was dispersed in deionized waterto obtain an anode slurry. The anode slurry was coated onto both sidesof a copper foil, which was then subjected to oven drying, calanderingand oven drying, followed by welding of nickel lead wires by anultrasonic welder to obtain the anode plate, the thickness of the platebeing in the range of 120-150 μm.

Preparation of the separator: a three-layer separator of polypropylene,polyethylene and polypropylene was used, the thickness being 20 μm.

Battery assembling: the three-layer separator having a thickness of 20μm was placed between the cathode plate and the anode plate, and theresulting sandwich structure composed of the cathode plate, the anodeplate and the separator was wound. The wound structure was flattened andplaced into an aluminum foil packing bag, and baked at 85° C. for 24hours to obtain a battery core, which was to be injected withelectrolyte. Then, the battery core was injected with an electrolyteprepared as above, and was vacuum-packed and allowed to stand for 24hours.

Battery formation: 0.05C constant current charging for 180 min, 0.1Cconstant current charging to 3.95V, vacuum packing again and standing at45° C. for 48 h, then further, 0.2C constant current charging to 4.4V,and 0.2C constant current discharging to 3.0V.

The batteries having the respective electrolytes in this technicalsolution were subjected to capacity retention rate test of 1C cyclingfor 400 cycles at 45° C., and capacity retention rate, capacity recoveryrate, and thickness expansion rate tests after storage at 60° C. for 30days. By “after storage at 60° C. for 30 days” was meant for theelectrolytes of the Comparative Examples, the lithium-ion batteries weretested after storage at 60° C. for 30 days, and the Test Examples weretested after storage at 60° C. for 30 days. The specific test methodsare as follows:

(1) The capacity retention rate test of 1C cycling for 400 cycles at 45°C. was in fact to measure the high-temperature cycling performance ofthe battery. The specific test method comprised: subjecting, at 45° C.,the formed battery to 1C constant current and constant voltage chargingto 4.35V, with the cut-off current being 0.01C, followed by 1C constantcurrent discharging to 3.0V. This was conducted for 400 cycles. Theformula for calculating the capacity retention rate is as follows:Capacity retention rate (%)=(discharge capacity at the 400^(th)cycle/discharge capacity at the 1^(st) cycle)×100%.

(2) The test method of capacity retention rate, capacity recovery rateand thickness expansion rate after storage at 60° C. for 30 dayscomprised: subjecting, at a normal temperature, the formed battery to 1Cconstant current constant voltage charging to 4.4 V, with the cut-offcurrent being 0.01C; followed by 1C constant current discharging to 3.0V, at which time the initial discharge capacity of the battery wasmeasured, followed by 1C constant current constant voltage charging to4.4V, with the cut-off current being 0.01C, at which time the initialthickness of the battery was measured; followed by storage of thebattery at 60° C. for 30 days, at which time the thickness of thebattery was measured; followed by 1C constant current discharging to3.0V, at which time the retention capacity of the battery was measured;followed by 1C constant current constant voltage charging, with thecut-off current being 0.01C; and followed by 1C constant currentdischarging to 3.0 V, at which time the recovery capacity was measured.The formulas for calculations are as follows:Battery capacity retention rate (%)=retention capacity/initialcapacity×100%Battery capacity recovery rate (%)=recovery capacity/initialcapacity×100%Battery thickness expansion rate (%)=(thickness after 30 days−initialthickness)/initial thickness×100%.

(3) Low-Temperature Discharge Performance Test:

At 25° C., the formed battery was subjected to 1C constant currentconstant voltage charging to 4.4 V, followed by constant voltagecharging until the current decreased to 0.01C, followed by 1C constantcurrent discharging to 3.0 V, at which time the normal-temperaturedischarge capacity was recorded. Then, the battery was subjected to 1Cconstant current charging to 4.4 V, followed by constant voltagecharging until the current decreased to 0.01C, followed by allowing thebattery to stand in an environment of −20° C. for 12 hours, and followedby 0.2C constant current discharging to 3.0 V, at which time thedischarge capacity at −20° C. was recorded.Low-temperature discharge efficiency at −20° C.=0.2C discharge capacity(−20° C.)/1C discharge capacity (25° C.)×100%

The test results are shown in Table 4.

TABLE 4 Test results 0.2 C Storage at 60° C. for 30 days discharge 400cycles Capacity Capacity Thickness efficiency at retention recoveryexpansion at 45° C. rate rate rate −20° C. Example 19 80.1% 83.4% 88.5%17.8% 72.6% Example 20 84.1% 85.6% 90.1% 15.5% 65.5% Example 21 80.5%84.6% 89.1% 16.5% 76.5% Example 22 79.5% 81.4% 86.7% 19.1% 76.8% Example23 76.6% 78.6% 84.2% 20.2% 70.1% Example 24 78.6% 80.2% 86.1% 18.2%69.4% Example 25 82.2% 84.6% 88.1% 16.1% 70.3% Example 26 81.4% 82.4%87.3% 21.8% 70.4% Example 27 80.5% 84.6% 89.3% 16.2% 71.2% Example 2885.5% 85.2% 91.1% 14.4% 74.1% Example 28 85.7% 88.6% 94.8% 13.2% 74.9%Example 30 82.1% 83.4% 88.7% 17.4% 76.2% Example 31 87.6% 88.7% 94.3%10.4% 73.6% Example 32 83.4% 84.6% 89.5% 18.2% 70.1% Example 33 86.4%86.5% 91.8% 15.6% 75.1% Example 34 83.5% 84.6% 89.4% 18.5% 75.3% Example35 88.4% 87.8% 94.1% 12.5% 74.1% Example 36 86.5% 90.7% 95.4% 13.2%70.3% Example 37 88.7% 89.2% 94.6% 13.1% 75.2% Example 38 83.4% 84.2%89.6% 13.6% 76.3% Comparative   40% 44.5% 50.1% 53.4%   76% Example 3Comparative 34.3% 35.2% 40.5% 70.4%   78% Example 4 Comparative 50.5%53.5% 60.3% 63.4%   75% Example 5 Comparative 30.1% 60.1% 68.4% 40.1%  70% Example 6 Comparative 62.1% 73.4% 78.6% 25.3%   30% Example 7Comparative 52.6% 65.8% 71.5% 32.4%   35% Example 8

It can be seen from the test results in Table 4 that compared with thecarbonate solvent, although the fluorinated solvent could improve thehigh-temperature cycling performance and the low-temperature dischargeperformance of the battery, the gas production during high-temperaturestorage was high, which was a safety hazard. Although the unsaturatedphosphate and/or the cyclic carboxylic anhydride additive couldsimultaneously improve the high-temperature cycling performance and thehigh-temperature storage performance, the extent of improvement waslimited and needed to be further increased, and moreover thelow-temperature discharge performance was poor. The combination of thefluorinated solvent with the unsaturated phosphate and/or the cycliccarboxylic anhydride could significantly improved the high-temperaturestorage performance and the high-temperature cycling performance of thebattery, without compromising the low-temperature discharge performance.Since there is a certain synergistic effect between the fluorinatedsolvent and the unsaturated phosphate and/or cyclic carboxylicanhydride, an effect not achievable with the respective single componentcan be obtained. Further addition of the unsaturated cyclic carbonate orthe cyclic sultone or the cyclic sulfate could further improve thehigh-temperature storage performance and the high-temperature cyclingperformance of the battery.

Technical Solution III:

In a series of studies on the electrolyte, it was found that the firstcompound, when used as a non-aqueous organic solvent, decomposes andproduces gas at the anode, which poses a safety hazard; and although thesecond compound can improve the high-temperature performance, itundergoes polymerization reaction on the surface of the cathode and theanode to form a passivation film, which has a high impedance, resultingin reduction in the low-temperature discharge performance and the rateperformance of the battery. After extensive research andexperimentation, the present applicant proposed that the first compoundand the second compound are used in combination to act in synergy, suchthat the respective advantages and functions of the first compound andthe second compound are maintained, and at the same time, the safetyhazard of the first compound decomposing at the anode to produce gas isovercome and the influence of the second compound on the low-temperaturedischarge performance and the rate performance of the battery isalleviated, which greatly improves the performances of the battery.

Electrolytes were prepared according to the components and ratios shownin Table 5, in which a plurality of non-aqueous electrolytes forlithium-ion battery according to the present application and a pluralityof comparative examples were designed, as shown in detailed in Table 5.

The respective electrolyte in this technical solution was prepared bypreparing a non-aqueous organic solvent in the proportion shown in Table5, then adding lithium hexafluorophosphate to the solvent to a finalconcentration of 1.0 mol/L, and then adding the additive according toTable 5. The percentage in Table 5 was percentage by weight, i.e., thepercentage of the additive based on the total weight of the electrolyte.The lithium salt content in the electrolyte was 12.5%, the other beingsolvent-grade additive.

TABLE 5 The components and amounts thereof in the electrolyte Totalcontent, Compound of composition and weight structure formula 4 Otheradditive and ratio of the solvent and amounts thereof amounts thereofComparative Content: 86.5% Tripropargyl — Example 9 EC/DEC = 1/2phosphate: 1% Comparative Content: 87.5% — — Example 10 EC/DFEA = 1/2Comparative Content: 86.5% — Tris(hexafluoroisopropyl) Example 11EC/DFEA = 1/2 phosphate: 1% Comparative Content: 86.5% —Tris(trifluoroethyl)phosphate: Example 12 EC/DFEA = 1/2 1% ComparativeContent: 86.5% — Tris(isopropyl)phosphate: Example 13 EC/DFEA = 1/2 1%Comparative Content: 86.5% — Tris(hexafluoroisopropyl) Example 14FEC/DFEA = 1/2 phosphate: 1% Comparative Content: 86.5% —Tris(hexafluoroisopropyl) Example 15 FEC/DFEA = 1/3 phosphate: 1%Comparative Content: 86.5% — Tris(hexafluoroisopropyl) Example 16EC/FEC/DFEA = 1/1/2 phosphate: 1% Comparative Content: 86.5% —Tris(hexafluoroisopropyl) Example 17 PC/FEC/DFEA = 1/1/2 phosphate: 1%Example 39 Content: 86.5% Tripropargyl — EC/DFEA = 1/2 phosphate: 1%Example 40 Content: 86.5% Tripropargyl — EC/DFEP = 1/2 phosphate: 1%Example 41 Content: 86.5% Di(propargyl)ethyl — EC/DFEA = 1/2 phosphate:1% Example 42 Content: 86.5% Di(propargyl)hexafluoroisopropyl — EC/DFEA= 1/2 phosphate: 1% Example 43 Content: 86.5% Tripropargyl — FEC/DFEA =1/2 phosphate: 1% Example 44 Content: 86.5% Tripropargyl — FEC/DFEA =1/3 phosphate: 1% Example 45 Content: 86.5% Tripropargyl — EC/FEC/DFEA =1/1/2 phosphate: 1% Example 46 Content: 86.5% Tripropargyl — PC/FEC/DFEA= 1/1/2 phosphate: 1% Example 47 Content: 86.5% Di(propargyl)ethylPC/FEC/DFEA = 1/1/2 phosphate: 1% Example 48 Content: 86.5%Di(propargyl)hexafluoroisopropyl PC/FEC/DFEA = 1/1/2 phosphate: 1%Example 49 Content: 86.5% Tripropargyl PC/FEC/DFPA = 1/1/2 phosphate: 1%Example 50 Content: 86.5% Tripropargyl PC/FEC/DFEP = 1/1/2 phosphate: 1%Example 51 Content: 86.5% Tripropargyl PC/FEC/DFPP = 1/1/2 phosphate: 1%Example 52 Content: 86.5% Tripropargyl — SL/FEC/DFEA = 1/1/2 phosphate:1% Example 53 Content: 86.5% Tripropargyl — GBL/FEC/DFEA = 1/1/2phosphate: 1% Example 54 Content: 85.5% Tripropargyl PS: 1% PC/FEC/DFEA= 1/1/2 phosphate: 1% Example 55 Content: 85.5% Tripropargyl BS: 1%PC/FEC/DFEA = 1/1/2 phosphate: 1% Example 56 Content: 85.5% TripropargylPST: 1% PC/FEC/DFEA = 1/1/2 phosphate: 1% Example 57 Content: 85.5%Tripropargyl MMDS: 1% PC/FEC/DFEA = 1/1/2 phosphate: 1% Example 58Content: 85.5% Tripropargyl DTD: 1% PC/FEC/DFEA = 1/1/2 phosphate: 1%Example 59 Content: 85.5% Tripropargyl CA: 1% PC/FEC/DFEA = 1/1/2phosphate: 1%

In the lithium-ion batteries in this technical solution, the cathodeactive material used was LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂, the anode usedwas graphite and conductive carbon black, and the separator used was athree-layer separator of polypropylene, polyethylene and polypropylene.Specifically, lithium-ion batteries were made as follows.

Preparation of the cathode: Cathode active materialLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂, conductive carbon black and binderpolyvinylidene fluoride were mixed in a mass ratio of 96.8:2.0:1.2. Themixture was dispersed in N-methyl-2-pyrrolidone to obtain a cathodeslurry. The cathode slurry was uniformly coated onto both sides of analuminum foil, which was then subjected to oven drying, calandering andvacuum drying, followed by welding of aluminum lead wires by anultrasonic welder to obtain the cathode plate, the thickness of theplate being in the range of 120-150 μm.

Preparation of the anode: Graphite, conductive carbon black and bindersstyrene-butadiene rubber and carboxymethyl cellulose were mixed in amass ratio of 96:1:1.2:1.8. The mixture was dispersed in deionized waterto obtain an anode slurry. The anode slurry was coated onto both sidesof a copper foil, which was then subjected to oven drying, calanderingand oven drying, followed by welding of nickel lead wires by anultrasonic welder to obtain the anode plate, the thickness of the platebeing in the range of 120-150 μm.

Preparation of the separator: a three-layer separator of polypropylene,polyethylene and polypropylene was used, the thickness being 20 μm.

Battery assembling: the three-layer separator having a thickness of 20μm was placed between the cathode plate and the anode plate, and theresulting sandwich structure composed of the cathode plate, the anodeplate and the separator was wound. The wound structure was flattened andplaced into an aluminum foil packing bag, and baked at 75° C. for 48hours to obtain a battery core, which was to be injected withelectrolyte. Then, the battery core was injected with an electrolyteprepared as above, and was vacuum-packed and allowed to stand for 24hours.

Battery formation: 0.05C constant current charging for 180 min, 0.1Cconstant current charging to 3.95V, vacuum packing again and standing at45° C. for 48 h, then further, 0.2C constant current charging to 4.4V,and 0.2C constant current discharging to 3.0V.

The lithium-ion batteries having the respective electrolytes in thistechnical solution were subjected to the test for the number of cycleswhen the capacity retention rate decreased to 80% during 1C cycling at45° C., and the tests for the capacity retention rate, capacity recoveryrate, and thickness expansion rate after storage at 60° C. for 14 days,wherein storage at 60° C. for a number of days means that thelithium-ion batteries comprising the respective electrolytes in theComparative Examples were tested after storage at 60° C. for 7 days, andthe lithium-ion batteries comprising the respective electrolytes in theExamples were tested after storage at 60° C. for 14 days. The specifictest methods are as follows:

The number of cycles when the capacity retention rate decreased to 80%during 1C cycling at 45° C. in fact represented the high-temperaturecycling performance of the battery. The specific test method comprised:subjecting, at 45° C., the formed battery to 1C constant current andconstant voltage charging to 4.4V, with the cut-off current being 0.01C,followed by 1C constant current discharging to 3.0V. This cycling wasconducted until the capacity retention rate decreased to 80%, at whichtime the number of cycles was counted. The formula for calculating thecapacity retention rate is as follows:Capacity retention rate (%)=(discharge capacity at the N^(th)cycle/discharge capacity at the 1^(st) cycle)×100%.

(2) The test method of capacity retention rate, capacity recovery rateand thickness expansion rate after storage at 60° C. for 14 dayscomprised: subjecting, at a normal temperature, the formed battery to 1Cconstant current constant voltage charging to 4.4 V, with the cut-offcurrent being 0.01C; followed by 1C constant current discharging to 3.0V, at which time the initial discharge capacity of the battery wasmeasured, followed by 1C constant current constant voltage charging to4.4V, with the cut-off current being 0.01C, at which time the initialthickness of the battery was measured; followed by storage of thebattery at 60° C. for 14 days, at which time the thickness of thebattery was measured; followed by 1C constant current discharging to3.0V, at which time the retention capacity of the battery was measured;followed by 1C constant current constant voltage charging, with thecut-off current being 0.01C, and followed by 1C constant currentdischarging to 3.0V, at which time the recovery capacity was measured.The formulas for calculation are as follows:Battery capacity retention rate (%)=retention capacity/initialcapacity×100%Battery capacity recovery rate (%)=recovery capacity/initialcapacity×100%Battery thickness expansion rate (%)=(thickness after 14 days−initialthickness)/initial thickness×100%.

(3) Low-Temperature Discharge Performance Test

At 25° C., the formed battery was subjected to 1C constant currentconstant voltage charging to 4.4 V, followed by constant voltagecharging until the current dropped to 0.01 C, followed by 1C constantcurrent discharging to 3.0 V, at which time the discharge capacity atnormal temperature was recorded. Then, the battery was subjected to 1Cconstant current charging to 4.4V, followed by constant voltage charginguntil the current dropped to 0.01 C, followed by allowing the battery tostand in an environment of −20° C. for 12 hours, followed by 0.2Cconstant current discharging to 3.0 V, at which time the dischargecapacity at −20° C. was recorded.Low-temperature discharge efficiency at −20° C.=0.2C discharge capacity(−20° C.)/1C discharge capacity (25° C.)×100%.

The test results are shown in Table 6.

TABLE 6 Test results Number of cycles when the capacity retention ratedecreased to 80% Storage at 60° C. for 14 days 0.2 C during 1 C CapacityCapacity Thickness discharge cycling at retention recovery expansionefficiency 45° C. rate rate rate at −20° C. Comparative 290   47%   51%  15%   40% Example 9 Comparative 250 20.1% 25.3%   42% 77.5% Example 10Comparative 365 78.2% 82.3% 20.6% 73.4% Example 11 Comparative 354 76.4%80.7% 24.5% 72.5% Example 12 Comparative 330 74.4% 78.6% 28.4% 73.2%Example 13 Comparative 400 80.5% 84.5% 32.4% 74.1% Example 14Comparative 387 79.5% 84.1% 27% 73.2% Example 15 Comparative 390 80.1%84.7% 26.4% 71.3% Example 16 Comparative 420 82.1% 87.2% 26.5% 74.5%Example 17 Example 39 430 83.5% 87.5% 12.4% 68.1% Example 40 445 84.5%88.4% 11.8% 69.4% Example 41 425 81.2% 85.1% 14.4% 72.5% Example 42 42079.1% 84.6% 16.5% 73.9% Example 43 510 85.2% 89.3% 18.2% 70.5% Example44 505 84.6% 89.1% 15.7% 72.1% Example 45 526 86.7% 90.5% 15.5% 71.6%Example 46 574 88.1% 92.2% 13.5% 73.4% Example 47 554 86.3% 90.7% 14.8%74.5% Example 48 535 84.4% 88.4% 16.6% 75.1% Example 49 589 88.9% 92.6%12.5% 73.6% Example 50 612 90.1% 94.2% 12.1% 74.6% Example 51 631 91.1%95.2% 11.5% 75.1% Example 52 512 83.1% 87.5% 20.5% 65.3% Example 53 52284.4% 88.5% 17.5% 64.2% Example 54 590 89.5% 93.5% 12.1% 70.4% Example55 595 89.2% 93.7% 13.3% 70.8% Example 56 620 90.5% 94.9% 12.4% 68.5%Example 57 650 90.9% 95.2% 12.3% 74.1% Example 58 655 90.5% 94.5% 13.6%76.2% Example 59 662 89.4% 92.1% 11.1% 69.6%

According to the results in Table 6, it can be seen that in ComparativeExample 9 that only used the second compound as an additive and did notuse the first compound as a solvent, the high-temperature cyclingperformance was weak, the capacity retention rate left was 80% after 290cycles, and the storage capacity and recovery capacity after storage at60° C. for 14 days were not satisfactory either, especially thelow-temperature discharge performance was relatively poor. InComparative Example 10 that used the first compound as a solvent and didnot use the second compound as an additive, the high-temperature storageperformance and the high-temperature storage performance were both verypoor. In Comparative Example 11-17 that used the first compound as asolvent, used saturated phosphate as an additive, and also optimized thesolvent combination, although the high-temperature cycling performanceand the high-temperature storage performance of the batteries weregreatly improved, the batteries still failed to meet the requirements,needed to be further improved. In Examples 39-59 that used the firstcompound as a solvent and the second compound as an additive and alsooptimized the solvent combination and the additive combination, thehigh-temperature cycling performance and the high-temperature storageperformance were both markedly improved, without compromising thelow-temperature discharge performance. In Example 59, thehigh-temperature cycling performance was the best, reduction of thecapacity retention rate to 80% only resulted after 662 cycles, and thehigh-temperature storage performance was also excellent.

The above is a further detailed description of the present applicationin conjunction with particular embodiments, and the specificimplementation of the present application is not to be construed aslimiting to such description. It will be apparent to those skilled inthe art that several simple derivations and substitutions can be madewithout departing from the concept of the present application and suchderivations and substitutions shall be deemed to fall within the scopeof protection of the present application.

The invention claimed is:
 1. A non-aqueous electrolyte for lithium-ionbattery, comprising Component A and Component B; wherein Component Aincludes at least one selected from the group consisting of thefluorinated cyclic carbonates represented by Structural Formula 1, andalso includes at least one selected from the group consisting of thealkyl-substituted cyclic carbonates represented by Structural Formula 2and/or at least one selected from the group consisting of thefluorinated carboxylates represented by Structural Formula 3; andComponent B includes at least one selected from the group consisting ofthe unsaturated phosphates represented by Structural Formula 4 and/or atleast one selected from the group consisting of the cyclic carboxylicanhydrides represented by Structural Formula 5;

wherein R₁ is a fluorine element or a fluorine-containing hydrocarbongroup having 1 to 4 carbon atoms, and R₂, R₃ and R₄ are eachindependently selected from a hydrogen element, a fluorine element, ahydrocarbon group having 1 to 4 carbon atoms or a fluorine-containinghydrocarbon group having 1 to 4 carbon atoms;

wherein R₅ is an alkyl group having 1 to 4 carbon atoms, and R₆, R₇ andR₈ are each independently selected from a hydrogen element or an alkylgroup having 1 to 4 carbon atoms;R₉COOR₁₀,  Structural Formula 3 wherein R₉ and R₁₀ are eachindependently selected from a hydrocarbon group having 1 to 4 carbonatoms or a fluorinated hydrocarbon group having 1 to 4 carbon atoms, andat least one of R₉ and R₁₀ is the fluorinated hydrocarbon group; and thefluorinated hydrocarbon group contains at least two fluorine atoms;

wherein R₁₁ is an unsaturated hydrocarbon group having 1 to 4 carbonatoms, and R₁₂ and R₁₃ are each independently selected from a saturatedhydrocarbon group having 1 to 4 carbon atoms, an unsaturated hydrocarbongroup having 1 to 4 carbon atoms or a fluorinated hydrocarbon grouphaving 1 to 4 carbon atoms;

wherein R₁₄ is selected from the group consisting of an alkylene groupor alkenylene group having 2 to 4 carbon atoms, or a fluorine-containingalkylene group or fluorine-containing alkenylene group having 2 to 4carbon atoms.
 2. The non-aqueous electrolyte according to claim 1,wherein Component A accounts for 10-90% of the total weight of thenon-aqueous electrolyte, and Component B accounts for 0.1-3% of thetotal weight of the non-aqueous electrolyte; wherein the compoundrepresented by Structural Formula 1 accounts for 5%-80% of the totalweight of the non-aqueous electrolyte, and the compound represented byStructural Formula 2 accounts for 5%-80% of the total weight of thenon-aqueous electrolyte, the compound represented by Structural Formula3 accounts for 5%-80% of the total weight of the non-aqueouselectrolyte, the compound represented by Structural Formula 4 accountsfor 0.1%-3% of the total weight of the non-aqueous electrolyte, and thecompound represented by Structural Formula 5 accounts for 0.1%-3% of thetotal weight of the non-aqueous electrolyte.
 3. The non-aqueouselectrolyte according to claim 1, wherein the fluorinated cycliccarbonates represented by Structural Formula 1 are one or more selectedfrom the group consisting of the compounds represented by Formula 1-1,Formula 1-2, Formula 1-3, and Formula 1-4:

wherein the alkyl-substituted cyclic carbonates represented byStructural Formula 2 are one or more selected from the group consistingof the compounds represented by Formula 2-1, Formula 2-2, and Formula2-3:

wherein the fluorinated carboxylate represented by Structural Formula 3is at least one selected from the group consisting of H₃CCOOCH₂CF₂H,H₃CH₂CCOOCH₂CF₂H, HF₂CH₂CCOOCH₃, HF₂CH₂CCOOCH₂CH₃, HF₂CH₂CH₂CCOOCH₂CH₃,H₃CCOOCH₂CH₂CF₂H, H₃CH₂CCOOCH₂CH₂CF₂H, CH₃COOCH₂CF₃, HCOOCH₂CHF₂,HCOOCH₂CF₃, and CH₃COOCH₂CF₂CF₂H; The non-aqueous electrolyte accordingto claim 1, wherein the unsaturated phosphate represented by StructuralFormula 4 is at least one selected from the group consisting oftripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethylphosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethylphosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropylphosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethylphosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate,diallyl 2,2,2-trifluoroethyl phosphate, diallyl 3,3,3-trifluoropropylphosphate, or diallyl hexafluoroisopropyl phosphate; wherein the cycliccarboxylate anhydride represented by Structural Formula 5 is at leastone selected from the group consisting of maleic anhydride, 2-methylmaleic anhydride, succinic anhydride, and glutaric anhydride.
 4. Thenon-aqueous electrolyte according to claim 1, wherein the non-aqueouselectrolyte further comprises at least one selected from the groupconsisting of an unsaturated cyclic carbonate, a cyclic sultone, and acyclic sulfate; and the unsaturated cyclic carbonate compound accountsfor 0.1% to 5% of the total weight of the non-aqueous electrolyte, thecyclic sultone compound accounts for 0.1% to 5% of the total weight ofthe non-aqueous electrolyte, and the cyclic sulfate compound accountsfor 0.1% to 5% of the total weight of the non-aqueous electrolyte;wherein the unsaturated cyclic carbonate is at least one selected fromthe group consisting of vinylene carbonate and vinylethylene carbonate;the cyclic sultone is at least one selected from the group consisting of1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone andmethylene methanedisulfonate; and the cyclic sulfate is one or moreselected from the group consisting of the compounds represented by thefollowing structures:


5. The non-aqueous electrolyte according to claim 3, wherein the firstcompound is at least one selected from the group consisting ofH₃CCOOCH₂CF₂H, H₃CH₂CCOOCH₂CF₂H, HF₂CH₂CCOOCH₃, HF₂CH₂CCOOCH₂CH₃,HF₂CH₂CH₂CCOOCH₂CH₃, H₃CCOOCH₂CH₂CF₂H, H₃CH₂CCOOCH₂CH₂CF₂H,CH₃COOCH₂CF₃, HCOOCH₂CHF₂, HCOOCH₂CF₃, and CH₃COOCH₂CF₂CF₂H; wherein thesecond compound is at least one selected from the group consisting oftripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethylphosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethylphosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropylphosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethylphosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate,diallyl 2,2,2-trifluoroethyl phosphate, diallyl 3,3,3-trifluoropropylphosphate, or diallyl hexafluoroisopropyl phosphate.